The lauric fats are composed of members of the seed fats of the palmae family which with very few exceptions consist of glycerides of a varied mixture of saturated fatty acids with unusually little in variation of composition throughout the whole family, lauric acid forming approximately half of the total fatty acids of most of the endosperm fats, with myristic acid amounting to about 20% and with significant, but smaller quantities, of capric and caprylic acids, the amount of palmitic and stearic acids being relatively small at less than 10% and 5% respectively and the amount of C.sub.18 fatty acids generally being substantially less than most vegetable fats and oils, particularly of polyunsaturared fatty acids containing two or more double bonds.
The lauric fats comprise a limited number of members of the family containing less than 20% total unsaturated fatty acids, their overall fatty acid composition providing a melting profile for which these fats are highly prized in confectionery, the principal members available in commercial quantities for this purpose being babassu, coconut and palm kernel fats, although others such as tucum and ucuhuba are also suitable for this purpose. In particular, coconut oil and stearin fractions derived from it by separating its lower-melting glycerides, are widely used in confectionery. Usually 50-75% of the lower-melting components are removed in an olein fraction, commonly by expressing it from the higher-melting stearin fraction under pressure. Alternatively, lauric fats may be hydrogenated to produce harder fats. It has however hitherto been the practice to hydrogenate non-selectively, usually with the aid of an active nickel catalyst, yielding a substantially saturated fat. The melting point of coconut oil when saturated is increased from 23.degree.-25.degree. to approximately 34.degree. C. and palm kernel oil from 27.degree.-29.degree. to approximately 42.degree. C. These hydrogenated fats are valued as toffee fats and for biscuits and other confectionery purposes.
The effect of non-selective hydrogenation however by measuring the amount of stearic acid residues, is progressively to increase solid content index (SCI) of the fat both at 20.degree. C. and 30.degree. C., to a level which is either too high at 30.degree. C. or too low at 20.degree. C. compared with coconut oil stearin, a good quality sample of which may exhibit SCI values of as high as 70-80% or even more at 20.degree. C., and 2% or less at 30.degree. C.
The present invention provides selectively hydrogenated lauric fats. Selective hydrogenation does not effect substantially complete saturation to measure the amount of stearic acid residues, but converts di- and higher unsaturated fatty acids to mono-unsaturated acids. At the same time selective hydrogenation promotes isomerisation of cis-oleic acid to trans-oleic acid, otherwise known as elaidic acid having a higher melting point than the cis acid. Non-selective catalysts may of course be used under hydrogenation conditions which limit the extent of hydrogenation, leaving a product in which a degree of unsaturation remains and in which a modicum of cis/trans isomerisation may occur. However, by its nature non-selective catalysis activity is indiscriminate and capable of leaving polyunsaturated fatty acid residues in the product while at the same time substantially increasing the amount of saturated fatty acid and moreover inducing less trans isomerisation by comparison with selective catalysts.
This difference is reflected in a increase in hardness of the less pronounced products of the invention. The isomerisation is always incomplete, with cis- and trans-isomers in equilibrium. Nevertheless, the fats of this invention exhibit a trans content of preferably at least 25% by weight of the total unsaturated fatty acids present, and more preferably at least 50%. The upper limit of the trans acid content in these terms is of course determined by the cis-trans equilibrium that can be achieved, generally agreed to be of the order of 1:2 molar ratio, the absolute amount of trans acid being determined by the Iodine Value of the fat. Trans-containing i.e. trans-isomerised lauric fats are believed to be novel.